Geoscience Reference
In-Depth Information
Figure 23.5
Dust storm approaching Stratford, Texas, 1935 (NOAA George E. Marsh Album).
Gill (1996) notes that human intervention in the hy-
drological cycle around playa systems may accelerate the
desiccation of playas, lower water tables, reduce soil mois-
ture and reduce vegetation cover, thus increasing suscep-
tibility to wind erosion. Gill (1996) reviewed evidence of
accelerated aeolian erosion from anthropogenically des-
iccated playa systems from across the globe, including
the Great Konya Lake basin in Turkey, the Sambhar Salt
Lake basin in Rajastan, Kara Bogaz Gol in Turkmenistan
and Old Wives Lake in Saskatchewan. However, while the
draining of the Aral Sea on the border of Kazakhstan and
Uzbekistan is perhaps the best-known and largest example
of human activity resulting in increased dust storm activ-
ity (Micklin, 1988), the region with the most frequently
occurring problems was in the western USA. Here, Gill
(1996) found numerous examples of playa-generated dust
storms exacerbated by human activity, including in An-
telope Valley near Los Angeles and the Salton Sea in
southern California. Such disturbance of the hydrological
status of these playa systems is often due to the demand
for water resources for urban centres or irrigation, or be-
cause of the development of roads and communication
lines that block or divert inflow or drainage waters.
The largest single source of aeolian dust in North Amer-
ica was Owens (dry) Lake in California (Cahill
et al.
,
1996) and much of our understanding of the impacts of
human interference on hydrological and aeolian systems
has come from research conducted on these lake sedi-
ments in the last 30 years. In 1913 the City of Los Angeles
Department of Water and Power (LADWP) began build-
ing a 223 mile aqueduct to divert the Owens River away
from the 110 square mile Owens Lake to provide wa-
ter for the growing city of Los Angeles. With its main
source of water diverted the lake began to dry and by
1927 there remained little standing water beyond a cen-
tral brine pool. Evaporation of near-surface groundwater,
with high concentrations of arsenic (Ryu
et al.
, 2002), led
to the deposition of efflorescent salts that were extremely
erodible (Cahill
et al.
, 1996), and from the 1930s onwards
the lake and surrounding regions suffered from increas-
ingly severe dust storms in the spring and autumn as high
winds were channelled between the Sierra Nevada and
the White-Inyo mountain ranges. These dust storms are
heavily salt-laden and loaded with respirable PM
10
ma-
terial with concentrations measured over a 2 hour period
exceeding 40 000 µg/m
3
(Cahill
et al.
, 1996) in compar-
ison with the US federal 24 hour air quality standard of
150 µg/m
3
. Estimates of the amount of eroded PM10 ma-
terial vary from 540 000 tons per year to 4000 000 tons per
year (GBUAPCD, 1994) and dust storms can reach as far
south as Los Angeles and Orange County (Figure 23.6),
covering an area >90 000 km
2
(Gill, 1996).
Since the early 1980s the Great Basin Unified Air Pollu-
tion Control District (GBUAPCD) has been coordinating
efforts to reduce dust emission to within federal limits.
Research has shown that, rather than the whole area of
the dry lake being susceptible to erosion, dust originates
from specific areas where a complex suite of conditions
interact to promote the availability of erodible material.
Gill (1996) lists the six conditions necessary as: saline
